1. Field of the Invention
The present invention relates to a packaged semiconductor, and more particularly, to packaged semiconductor devices and integrated circuits for removing excess heat from the devices and integrated circuits.
2. Description of the Related Art
Generally, semiconductor devices include and are not limited to integrated circuit (IC) devices, diodes, thyristors, or MOS gate devices, for example, metal-oxide-semiconductor field effect transistors (MOSFET) and insulated gate bipolar transistors (IGBT). Each are formed in a silicon semiconductor die. In vertical MOSFET devices, the die includes a metal drain electrode at its lower portion, and a metal source electrode, and a gate electrode on its top surface. In that special case, the die pad of the MOSFET may also be a lead. The device die or IC die is attached to a surface of a leadframe pad, and electrodes on the die are electrically connected to leads of the leadframe by a wire bonding. The leadframe temporarily holds the leads in place. A typical leadframe has two parallel rails with a number of cross rails. A die pad in the center is supported by tie bars that extend from the rails toward the center of the frame. Other leads extend from The leads extend from the rails toward the center of the frame but do not support the die. Consequently, the electrodes on the die are electrically connected to proximate ends of leads of the leadframe. The distal ends of the leads protrude out of a molded housing. The silicon semiconductor die and the wire are completely molded in the housing.
A conflict arises since there is a demand for smaller and smaller semiconductor devices, while speed, power, and capacity are expected to increase. Various solutions have arisen to provide compromise solutions. For example, one problem that can arise is heat dissipation. Since electronic components, such as diodes and ICs, produce heat, it is important to have a way to remove heat from the components to prevent overheating, which can adversely affect performance of the components or even cause them to fail. Prior art arrangements offer heat dissipation arrangements, but it is always desirable to have more efficient heat dissipation allowing electronic components to operate at lower temperatures when feasible and not overly expensive.
An example of such a heat dissipation solution is shown in FIG. 1. In FIG. 1, a semiconductor device 10 includes a die 11 attached to a premolded leadframe 12 via a die attach die bonding material 13, such as an epoxy based bonding material. The premolded leadframe 12 includes a plurality of leads 14 and an attach area 15 on the top surface of the premolded leadframe 12 and is underfilled with a molding compound, such as an epoxy resin, electronic molding compound (EMC), or the like, so that the leads on the leadframe are supported by the material. The die 11 is attached to the attach area 15 via wires 22 bonded to the die 11 by known wire bonding techniques. The die 11, premolded leadframe 12, and bonded wires are encased in EMC and the leads are cut to form terminals 23 of the device 10. While the leads 14 and terminals 23 conduct heat away from the die 11 and transfer it to conductors to which they are attached, heat can still undesirably build up in the device 10 since the only heat path from the die to the leads is the premold material on the leadframe and the EMC applied to the entire assembly, reducing performance and possibly resulting in failure of the device 10.
Another approach is disclosed in U.S. Pat. No. 7,190,066 to Huang et al. in which a round top heat spreader is disposed over a die, but the spreader only extends part way across the die and the device as a whole. Further, the substrate does not allow for transfer of heat from the spreader to the bottom of the device since it employs ball grid array (BGA) balls and does not have leads extending through the entire depth of the substrate.
A further approach is disclosed in U.S. PreGrant Publication No. 20070132091 to Wu et al. in which an upper heat sink includes a depression over the die and is connected to the substrate by four leads. However, while there is dissipation via the top surface of the upper heat sink, no provision is made to conduct heat from the upper heat sink to the bottom of the device for enhanced heat dissipation.
Embodiments disclosed herein provide a thermally enhanced MLP that uses heat conductive material shaped into a heat spreader and placed in the MLP so as to conduct more heat away from the die embedded therein, enhancing performance and lengthening the life of the device. The heat spreader is preferably in thermal communication with at least one of the leads of the device and occupies at least a portion of the top of the device, allowing radiant cooling or connection of the spreader to heat pipes or other cooling arrangements. In one form, the spreader is simply a layer of thermally conductive material with projections extending toward the leadframe, at least one of the projections serving as a support during assembly and as a connector and thermal conduit from one or more of the leads. In another form, the heat spreader projections are eliminated save for the support/conduit/connector and a central heat collector positioned in the center of the spreader over the center of the die. The support/conduit/connector is sized so that the heat collector is spaced apart from the die, but can collect heat produced by the die and direct it to the top surface of the device. The top surface can then radiate heat or be connected to heat pipes or other cooling arrangements. Fins can be employed in embodiments to enhance cooling, such as by convection and radiation. The resulting device allows the die to operate at a lower temperature than prior arrangements.
Advantageously, an improved leadframe can be employed in embodiments to further enhance thermal communication between the die, the heat spreader, and the leadframe. The improved leadframe includes lead portions that are in direct thermal communication with the die and preferably also includes at least one enlarged lead in direct thermal communication with the heat spreader. The enlarged lead(s) provide additional heat carrying capacity to better dissipate heat transferred to the lead. The improved leadframe even further lowers operating temperature of the die.